1. Field of the Invention
The present invention relates to a stage apparatus which positions, in particular, a workpiece such as a semiconductor wafer or a reticle to a predetermined position or scans the workpiece at a predetermined speed in an exposure apparatus. The present invention also relates to a linear motor used for such a stage apparatus, and an exposure apparatus and device production method using such a stage apparatus.
2. Related Background Art
FIG. 31 is a view showing a conventional semiconductor exposure apparatus to which the present invention is applied. This exposure apparatus is a so-called scan type exposure apparatus in which an image of only an arcuate or rectangular region of a reticle pattern, i.e., an original pattern is formed on a wafer as an exposure target, and both the reticle and the wafer are mechanically scanned to expose the entire reticle pattern. FIGS. 32 and 33 are perspective views showing details of a reticle scanning system. FIG. 32 shows a system in which a driving system is arranged on one side of the reticle stage. FIG. 33 shows a system in which driving systems are arranged on both sides of the reticle stage, i.e., on both sides of the optical axis.
Referring to FIG. 31, a main body table 102 is supported on a reference base 100 through an anti-vibration means 101. A wafer stage 103 is mounted on the main body table 102 to be movable within the X-Y plane (horizontal plane). A projection optical system 106 is fixed above the wafer stage 103 through a main body supporting member 105. A reticle stage base 80, and a reticle stage 82 capable of uniaxially scanning on the reticle stage base 80 along a guide (not shown), are arranged above the supporting member 105. An interferometer second reference 104 is used to measure the position of the wafer stage 103. An interferometer first reference 107 is used to measure the position of the reticle stage 82. An illumination system 108 supplies an exposure energy to a wafer (not shown) on the wafer stage 103 through a reticle (not shown) on the reticle stage 82.
Referring to FIG. 33, a guide 81 is fixed on the reticle stage base 80. The reticle stage 82 is supported on the guide 81 through a lubricating means such as an air film to be slidable in the scanning direction. A reticle 83 as a workpiece is held on the stage 82. Driving coils 85 are fixed on both sides of the reticle stage 82. Linear motor stators each comprising a yoke 86 and a permanent magnet 87 are arranged to apply predetermined magnetic fields perpendicular to the windings to part of the driving coils 85 over the entire stroke of the reticle stage 82. The linear motor stators are fixed on the reticle stage base 80. A power amplifier (not shown) is connected to the driving coil 85. A linear power amplifier which continuously flows a current corresponding to a command value is used, so that the power amplifier can respond to a current command up to high frequencies. The wafer stage 103 can have a similar arrangement as that of the reticle stage 82. The X-Y stage is constituted by stacking two driving mechanisms (stage apparatuses).
The permanent magnet 87 is magnetized in the direction of its thickness, as shown in FIG. 34. More specifically, the magnet surface contacting the yoke 86 is magnetized to an S pole, and the opposite magnet surface opposing part of the driving coil 85 is magnetized to an N pole. The driving coil 85 is kept separated from the yoke 86 and the permanent magnet 87, i.e., the linear motor stator, over the entire stroke of the reticle stage 82.
In the above arrangement, when the workpiece 83 such as a reticle or a wafer is to be moved, the linear power amplifier flows an accelerating current or a decelerating current to the driving coil 85 upon receiving a command from a position/speed control circuit (not shown). In positioning as well, the linear power amplifier continuously flows a small current to the driving coil 85 in correspondence with a command from a control circuit (not shown) such that the positional deviation of the stage 82 is eliminated at all times. That is, for both acceleration/deceleration and positioning, the identical power amplifier and driving coil 85 are used.
In the scan type exposure apparatus shown in FIG. 31, an illumination light beam is irradiated on the reticle on the reticle stage only in its elongated rectangular or arcuate region which is perpendicular to the scanning direction of the reticle stage 82. For this reason, when the entire reticle pattern is to be exposed on the wafer, both the reticle stage 82 and the wafer stage 103 must be scanned. The scanning operation is performed at a constant speed. The ratio of the speed of the reticle stage 82 to that of the wafer stage 103 during the scanning operation is made precisely equal to the reduction magnification of the projection optical system 106. The positions of the reticle stage 82 and the wafer stage 103 are measured by laser interferometers (not shown) through the interferometer first reference 107 and the interferometer second reference 104, respectively, and fed back to a control system (not shown).
In the above arrangement, the wafer stage 103 and the reticle stage 82 are moved to initial positions and accelerated. The acceleration is controlled to converge such that, before the wafer stage 103 and the reticle stage 82 enter the region where the illumination light beam is irradiated, they attain a predetermined positional relationship, and the speed ratio becomes equal to the reduction magnification of the projection optical system 108. An exposure operation is performed while maintaining this state. When the wafer stage 103 and the reticle stage 82 leave the region where the illumination light beam is irradiated, they are appropriately decelerated.
FIG. 35 is a perspective view showing another conventional art. This system differs from that shown in FIG. 32 in the arrangement of the single-phase linear motor. More specifically, the movable unit of the linear motor shown in FIG. 35 comprises a short magnet 95 with its one pole opposing a coil 98, a fixed yoke 96 arranged over the entire stroke of the movable magnet 95 to circulate the magnetic fluxes of the magnet 95, and a single-phase coil wound on part of the fixed yoke 96 over the entire stroke of the magnet 95.